With multi-rotor UAV and drone technologies, there are specific limitations on flight time, payload and aerodynamic control. Existing designs for machines based on these technologies make extensive use of multiple arms or outriggers on each of which a respective electric motor is mounted for rotating the respective head rotor. Configurations used include three, four, six or eight arms or outriggers as popular choices, although there are other arrangements that are possible. It is common for these configurations to utilise head rotors that generate thrust by fixed pitch rotary wings or rotor blades. As in all aeronautical applications, thrust is somewhat proportional to rotary wing or blade speed, ignoring efficiencies and specific aerodynamic specialties.
With machines operating with head rotors having such fixed pitch wings or blades, lift, yaw, pitch and roll are achieved by variation in the relative speed of selected electric motors. Thus, for a machine having a quadcopter arrangement of four motors, the speed of one opposed pair of motors can be varied relative to the other opposed pair of motors of the machine. However, particularly with yaw (also referred to as “pirouette”), functionality is compromised by such use of the electric motors. Yaw, or yaw rate, generally is achieved by speeding up or slowing down selected motors to generate a net torque about a central axis perpendicular to a plane in which the machine is travelling. Quite often responsiveness is slow or weak, as the extent to which selected motors are slowed down cannot be so great as to risk compromising the necessary overall lift imparted to the machine. The limited responsiveness is most evident when a multi-rotor machine is ascending or descending while also pirouetting. These simultaneous actions generally lead to clumsy movement or to compromises in flight characteristics.
Such limitations with current machines may be reduced, or even be overcome, as advances are made in electronic control or governance. However, even if this proves to be the case, the machines are likely to continue to be limited in terms of flight times. It is not uncommon for the electric motors of multi-rotor machines to be able to perform duties for not more than about 10 to 20 minutes, even with the optimum current lithium polymer batteries, while the flight performance over the operating time deteriorates as the battery charge level reduces with flight time. The current limited flight times able to be obtained with multi-rotor machines operating with individual electric motors are expected to continue into the future, restricting the range of applications in which the machines can be used effectively. There may be improvement in flight times as a result of advances in battery technology. However, it is unlikely that these times will double or quadruple, let alone increase by an order of magnitude as required to achieve significantly enhanced flight times.
The present invention is directed to providing an improved multi-rotor flying machine that, at least in the context of multi-rotor machines of the multi-copter type, including such machines suitable for use as a UAV or as a drone, enables the limitations discussed above to be reduced or overcome. However, the present invention also is applicable to manned aerial vehicles comprising helicopters having a number of head rotors each mounted for rotation around a respective mast.